Fluid Catalytic Cracking (FCC) is one of the largest secondary refining processes which employ most sophisticated zeolite based catalysts. With the increasing crude prices, refiners have been processing heavier feeds sourced from heavy vacuum gas oil, atmospheric bottom, coker naphtha containing metals ranging from 10-200 ppm and con-carbon up to 10 wt %. However, while processing of heavy feeds, catalyst can accumulate significant amount of metals.
Presence of contaminant metals on FCC catalysts is known to affect activity and selectivity. Though high metal tolerant catalysts are available in the market, for maintaining conversion, catalyst make-up rate is higher. Though polyaromatic con-carbon temporarily reduces activity while major activity can be restored by burning off coke, high temperature of exothermic coke combustion can permanently impair the activity of the catalyst.
The contaminant metals such as vanadium and sodium are known to permanently damage the key component of catalyst such as zeolite and matrix through reacting with framework aluminum, structure stabilizing rare earth components. Besides, vanadium metals are known to migrate from particle to particle at high temperature above 670° C. resulting in crippling of catalytic activity of even freshly added catalyst also. Nickel, although may not harm the structure of catalyst however, it is known to dehydrogenate valuable hydrocarbons during cracking reactions. This will result in significant increase in the amount of coke and dry gas. In view of this, catalyst replacement is most preferred in spite of being an expensive option.
U.S. Pat. No. 4,465,588 and U.S. Pat. No. 4,650,564 disclosed improvement of catalytic cracking of high metals content feed stocks such as, for example, those containing iron, vanadium nickel and copper by contacting said feed stocks under defined catalytic cracking conditions with a novel catalyst composition comprising a solid cracking catalyst and a controlled concentration of a diluents comprising alumina to increase gasoline yield and conversion. The concentration of nickel, vanadium and iron contaminants on said catalyst composite is in the range of 4000 to 20000 ppm and achieved following results with Kuwait gas oil (CCR-0.23 wt %, 260-427° C. cut). Although this patent has claimed that their alumina diluents can increase the conversion from (28-57) vol % to (54-70) vol %, however the same is a very low conversion if converted into wt % term in comparison to available prior art.
U.S. Pat. No. 7,008,896 is directed to a process for the preparation of crystalline anionic clay-containing bodies from sources comprising a trivalent metal source (aluminium, gallium, indium, iron, chromium, vanadium, cobalt, manganese, cerium, niobium and lanthanum) and divalent metal source (magnesium, zinc, nickel, copper, iron, cobalt, manganese, calcium, and barium) for the removal of SOx and/or NOx compound in FCC.
U.S. Pat. No. 4,956,075 describes the use of a catalyst containing Mn, a large pore crystalline molecular sieve, and optionally rare earth in catalytic cracking is disclosed. This catalyst gives high gasoline selectivity with low coke yields and is suitable for either gas oil or residue cracking applications.
Composition and methods disclosed in U.S. Pat. No. 7,993,623 B2 for removing poisonous metals from hydrocarbons comprise hydrotalcite having one or more trapping metals dispersed on the outer surface to increase gasoline yield, reduction of bottom and coke yields. The above samples are checked with metal level of nickel 3000 ppm and vanadium 3000 ppm only.
In light of the existing processes, there still exists a need to develop a composition for removal of metal and other contaminants from hydrocarbon feeds containing higher concentration of the contaminants.